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[css-view-transitions-1] Clarify how unhandled rejections should work #8451

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[css-view-transitions-1] Clarify how unhandled rejections should work #8451

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23 changes: 17 additions & 6 deletions css-view-transitions-1/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -936,8 +936,8 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
[Exposed=Window]
interface ViewTransition {
readonly attribute Promise<undefined> updateCallbackDone;
readonly attribute Promise<undefined> ready;
readonly attribute Promise<undefined> finished;
[SameObject] readonly attribute Promise<undefined> ready;
[SameObject] readonly attribute Promise<undefined> finished;
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@domenic domenic Feb 15, 2023

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This is not valid Web IDL, technically. whatwg/webidl#71

undefined skipTransition();
};
</xmp>
Expand Down Expand Up @@ -1009,15 +1009,23 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;

: <dfn>ready promise</dfn>
:: a {{Promise}}.
Initially [=a new promise=] in [=this's=] [=relevant Realm=].
Initially [=a new promise=] in [=this's=] [=relevant Realm=], [=marked as handled=].

Note: This is [=marked as handled=] to avoid {{unhandledrejection}}s prior to the {{ViewTransition/ready}} property being accessed.

: <dfn>update callback done promise</dfn>
:: a {{Promise}}.
Initially [=a new promise=] in [=this's=] [=relevant Realm=].

Note: This promise is not initially [=marked as handled=],
so rejections will be {{unhandledrejection}}s,
even if the {{ViewTransition/updateCallbackDone}} property is not accessed.

: <dfn>finished promise</dfn>
:: a {{Promise}}.
Initially [=a new promise=] in [=this's=] [=relevant Realm=].
Initially [=a new promise=] in [=this's=] [=relevant Realm=], [=marked as handled=].

Note: This is [=marked as handled=] to avoid {{unhandledrejection}}s prior to the {{ViewTransition/finished}} property being accessed.

: <dfn>transition root pseudo-element</dfn>
:: a ''::view-transition''.
Expand All @@ -1032,9 +1040,12 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
[Discussion of this behavior](https://github.com/w3c/csswg-drafts/issues/8045).
</dl>

The {{ViewTransition/finished}} [=getter steps=] are to return [=this's=] [=ViewTransition/finished promise=].
The {{ViewTransition/finished}} [=getter steps=] are to return [=a promise resolved with=] [=this's=] [=ViewTransition/finished promise=].
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@domenic domenic Feb 15, 2023

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This will return a new promise each time, since the getter steps are run each time. (Even if [SameObject] were allowed, it doesn't do magic caching behavior for you; it's more of a code comment. See whatwg/webidl#212.)

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@jakearchibald jakearchibald Feb 15, 2023

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Huh, TIL. I could have sworn I'd seen specs written assuming SameObject had this effect.


The {{ViewTransition/ready}} [=getter steps=] are to return [=a promise resolved with=] [=this's=] [=ViewTransition/ready promise=].

The {{ViewTransition/ready}} [=getter steps=] are to return [=this's=] [=ViewTransition/ready promise=].
Note: These properties return a new promise that is not [=marked as handled=].
They always return the same promise due to {{SameObject}}.

The {{ViewTransition/updateCallbackDone}} [=getter steps=] are to return [=this's=] [=ViewTransition/update callback done promise=].

Expand Down